More precisely, said device is intended to protect the aircraft from low energy situations (low speed, high incidence, weak engine thrust) which can threaten the safety of the aircraft, particularly close to the ground.
In general, such a device usually comprises:                triggerable control means, for activating, when they are triggered, a protective function consisting in automatically controlling said engines in order that each of them provides maximum thrust; and        triggering means to automatically monitor a plurality of parameters and to automatically trigger said control means when triggering conditions depending on said parameters are fulfilled.        
However, because of the generation of maximum thrust on each of the engines of the aircraft at the time of activation of the protective function, a problem arises in the event of a failure of one of these engines. In fact, in this case, said protective function causes a thrust unbalance, that is to say the thrust generated on one side (under one wing) of the aircraft is much greater than that generated on the other side (under the other wing). This gives rise to a large yaw movement which can result in difficult lateral control and therefore generate a large safely problem for the aircraft.
Also, in order to avoid such a situation, a protective device of said type generally furthermore comprises:                detecting means for detecting all of said engine failures; and        inhibiting means which are connected to said detecting means and which are able to inhibit said triggering means and therefore deactivate said protective function.        
Said inhibiting means are usually produced in such a way as to inhibit the triggering means as soon as one of the engines is detected as having failed by said detecting means, which makes it possible to avoid the aforesaid problems.
However, such a solution greatly reduces the availability of the protective device such that, as soon as at least one engine fails, the aircraft no longer has energy protection.